Transmitter-receiver for short-range wireless transmission

Abstract

The present invention provides a transmitter-receiver for short-range wireless transmission, which comprises a frequency scan signal receiving section that searches a vacant channel frequency by frequency scanning of a receiving wave, and a signal transmitting section that transmits a transmitting wave using the searched vacant channel frequency. The frequency scan signal receiving section sequentially changes a frequency of a PLL oscillator by control of a controller to thereby search the presence or absence of a receive frequency lying in a predetermined frequency band depending on an output state of a carrier detector. When the controller detects a vacant channel frequency, the frequency scan signal receiving section fixes the oscillation frequency of the PLL oscillator to an oscillation frequency corresponding to the vacant channel frequency and supplies the fixed oscillation frequency to the signal transmitting section. The signal transmitting section forms a transmit signal with the supplied oscillation frequency as a local oscillation signal and transmits the transmit signal having the same channel frequency as the vacant channel frequency as a transmitting wave.

1 . A transmitter-receiver for short-range wireless transmission, comprising:
 a frequency scan signal receiving section which searches a vacant channel frequency by frequency scanning of a receiving wave; and   a signal transmitting section which transmits a transmitting wave using the searched vacant channel frequency,   wherein the frequency scan signal receiving section sequentially changes an oscillation frequency of a local oscillator constituting a PLL by control of a controller to thereby search the presence or absence of a receive frequency lying in a predetermined frequency band depending on an output state of a carrier detector, and, when the controller detects a vacant channel frequency by the search thereof, fixes the oscillation frequency of the local oscillator to an oscillation frequency corresponding to the vacant channel frequency and supplies the fixed oscillation frequency to the signal transmitting section, and   wherein the signal transmitting section performs frequency conversion of a transmit signal using the supplied oscillation frequency as a local oscillation frequency to thereby form a transmit signal having the same channel frequency as the vacant channel frequency, and transmits the formed transmit signal as a transmitting wave.   
   
   
       2 . The transmitter-receiver for short-range wireless transmission according to  claim 1 , wherein the signal transmitting section includes a voltage-controlled oscillator whose oscillation signal is modulated by a modulation signal, and a modulator which frequency-mixes the modulated oscillation signal of the voltage-controlled oscillator and the oscillation frequency corresponding to the vacant channel frequency, and the modulator outputs a transmit signal having the same channel frequency as the vacant channel frequency therefrom. 
   
   
       3 . The transmitter-receiver for short-range wireless transmission according to  claim 2 , wherein the modulator is an analog multiplier. 
   
   
       4 . The transmitter-receiver for short-range wireless transmission according to  claim 1 , wherein the frequency scan signal receiving section includes a first frequency converting unit which frequency-mixes a received signal and an oscillation frequency of the local oscillator to form a first intermediate frequency signal, and a second frequency converting unit which frequency-mixes the first intermediate frequency signal and an oscillation frequency of a second local oscillator to form a second intermediate frequency signal. 
   
   
       5 . The transmitter-receiver for short-range wireless transmission according to  claim 1 , wherein the frequency scan signal receiving section includes variable control switch means which is provided between a demodulator circuit and a low frequency amplifier and selectively outputs a demodulated signal supplied from the demodulator circuit and a modulated signal supplied from the signal transmitting section to the low frequency amplifier, and
 wherein the controller supplies a switching voltage to the variable control switch means upon a search for a vacant channel frequency thereby to allow the variable control switch means to perform switching from the previously-taken output of the demodulated signal to the output of the modulated signal.